The increasing demands for very large-scale integrated circuits (VLSI) have made imperative the development of practical, reliable, multilevel metallization systems. In such systems, two layers of metal, generally aluminum or an aluminum alloy, are separated by a layer of insulating dielectric material which contains vias in a predetermined pattern. Because there is contact between two metal layers in the vias it is critical that they be cut cleanly to assure maximum contact with minimal resistance.
While a number of materials have been and are used for forming the insulating dielectric layer in such multilayer metallization systems, the current trend in the electronics industry is toward the use of polyimides. Vias are commonly formed in polyimide dielectric layers by oxygen plasma etching. Although effective, oxygen plasma etching is disadvantageous in that there is formed at the bottom of such vias a residual film of insulating material which interferes with metal-to-metal contact. A significantly efficient method of removing this film is provided in accordance with this invention.